The present invention relates to a semiconductor device molding a single or a plurality of integrated circuit chips with resin material.
In general, a resin-molded semiconductor device mounts an IC chip on a lead-frame made of a thin metal plate and molds such a chip with resin material using a transfer mold apparatus in applicability to mass production and low cost of semiconductor device. However, recent increase in packing density of IC chip and also brings about a problem of short-circuit of wires because an IC chip becomes smaller in size with the space between adjacent wires narrowed.
Wires are bonded from connecting pads, which are called as "chip-pads" hereinafter, of the IC chip to inner-leads which are parts, molded in resin, of the lead-frame. A problem of the short-circuiting can be solved by making short the bonded wires. Lengths of the bonded wires can be shortened to a certain degree by narrowing a distance between each chip-pad and a tip part of the inner-lead corresponding to the chip-pad, however, there is a limitation in such attempt, because a lead-frame is formed by etching or stamping technique and the space between the tip parts of the inner-leads cannot be narrowed as desired due to the relation to the required thickness, for example 0.15 millimeter (mm), of the lead-frame. Therefore, the distance between the chip-pad and the tip part of the inner-lead cannot be shortened excessively. Accordingly, shortening of wires was required and has been realized by providing relay-pads on the way from the chip-pads to the tip parts of corresponding inner-leads. A provisional publication in Japan SHO 56-100436 has disclosed about the relay-pads. According to the provisional publication, a conventional long wire 106 shown in FIG. 1 is divided into wires 206 and 306 by a relay-pad 107 as illustrated in FIGS. 2 and 3, which realizes substantially shortening the bonded wires.
Through FIGS. 1, 2 and 3, the same reference numerals designate the same parts. FIGS. 1 and 2 are schematic perspective views illustrating the lead-frame on which an IC chip is mounted. The IC chip 104 is mounted on a die-stage 102 which is a part of the lead-frame 103. In FIG. 1, the wire 106 is bonded between the chip-pad 105 on the IC chip 104 and the tip part of inner-lead 101 which is a part of the lead-frame 103. From FIG. 1, it will be clear that the wire 106 is so long that the trouble of the short-circuiting will occur. In FIG. 2, a plurality of relay-pads 107 are arranged surrounding the IC chip 104 on the die-stage 102 in order to avoid short-circuiting of the bonded wires. Accordingly, the wire 106 shown in FIG. 1 can be divided into the short wires 206 and 306 by the relay-pad 107. That is, because of providing the relay-pad 107, the length of wire can be shortened to a half or less of the length of usual wire such as the wire 106 in FIG. 1, so that the fear of short-circuiting can be eliminated. FIG. 3 is a partially schematic sectional views illustrating how the wires 206 and 306 are bonded. As shown in FIG. 3, the relay-pad 107 comprises an insulator 108 and a metal part 109. Namely, since a die-stage 102 is made of a metal material, the metal part 109 to which the wires 206 and 306 are bonded are provided on the die-stage 102 inserting the insulator 108. The relay-pad 107 is formed by partially coating insulation material onto the necessary places on the surface of the die-stage 102 for forming the insulator 108, depositing a metal on the coated insulator 108, and moreover partially etching the deposited metal in a form of the pad.
As described above, the bonded wires can be shortened by providing the relay-pads to the die-stage and a problem of short-circuit of the bonded wires is solved; however, there is another problem relating to the formation of the relay-pads on the die-stage. Since the lead-frame is made of thin metal plate, the lead-frame is easily deformed or damaged by mechanical force or heat added during the process of forming the relay-pads on the die-stage of lead-frame, resulting in lowering a yield rate of the semiconductor device. FIGS. 1, 2 and 3 illustrate the case where only one IC chip is mounted; however, when a plurality of IC chips are mounted, this problem becomes further distinctive because relay wires or relay electrodes connecting between IC chips may be newly required in addition to the relay-pads.